Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$198.30	11.538%	$221.1799	$221.18	$221.20	$221.20
Purchase #2	$81.58	8.489%	$88.5053	$88.51	$88.50	$88.50
Purchase #3	$234.92	12.453%	$264.1746	$264.17	$264.15	$264.20
Purchase #4	$46.50	3.501%	$48.128	$48.13	$48.15	$48.10
Purchase #5	$106.36	5.754%	$112.48	$112.48	$112.50	$112.50
Purchase #6	$111.48	6.606%	$118.8444	$118.84	$118.85	$118.80
Purchase #7	$146.38	3.410%	$151.3716	$151.37	$151.35	$151.40
7 purchase totals =	$925.52		$1,004.6838	$1,004.68	$1,004.70	$1,004.70